If the people selling it can't tell you much at all about it, I'd ask where they got it and see if you can get answers from their supplier.
Honestly, you could use things like plastic pot scrubbers from the $ store. There's lots of cheap substitutes before using something from a masonry supply yard that can't even tell you what it is.
Since you already bought it, the best I can suggest is to try and cycle a tank with it in a filter, test the heck out of it and see how some feeders do. But even if it looks / acts OK, you won't know how it will react / perform over time and at different Ph levels.
"Why can't my wife see all of this stuff as an investment?"